The present invention relates to an optical module for optically connecting an optical device and an optical waveguide provided on a substrate and, more particularly, to a structure for allowing the optical device to be accurately mounted to the substrate with respect to a reference plane without any adjustment.
An optical device mounting structure is disclosed in, e.g., Japanese Patent Laid-Open Publication No. 63-143890. In the structure taught in this document, an end-face emission type semiconductor laser including an active layer is mounted on a substrate. The substrate is formed with an optical waveguide. To guide a beam issuing from the laser to the waveguide, a recess slightly greater in size than the laser is formed in the substrate. Electrodes are positioned on the bottom of the recess in order to connect electrodes provided on the laser and connection members implemented by solder.
However, a problem with the above conventional structure is that the optical axis between the laser and the waveguide and the position in the vertical direction have their accuracy determined simply by the processing accuracy of the lug and the mounting accuracy of the laser to the lug. Because the lug and laser must be abutted against each other with preselected accuracy in height, the mounting accuracy is only of the order of several microns. Moreover, the laser is connected to the substrate by relying only on the connection members implemented by solder. As a result, it is likely that the optical axis of the laser is inclined in the horizontal direction and/or angularly displaced due to the fusing of the connection members, failing to align with the optical axis of the waveguide
In another conventional structure, a lug formed with fine grooves is positioned on the bottom of a recess formed in a substrate. A member having high thermal conductivity intervenes between and connects the surface of a semiconductor layer and the top of the lug in order to enhance heat radiation. However, it is extremely difficult to control the thickness of the above member and therefore to guarantee mounting accuracy.